Contrasting biological features in morphologically cryptic Mediterranean sponges

Abstract

Sponges are key organisms in the marine benthos where they play essential roles in ecological processes such as creating new niches, competition for resources, and organic matter recycling. Despite the increasing number of taxonomical studies, many sponge species remain hidden, whether unnoticed or cryptic. The occurrence of cryptic species may confound ecological studies by underestimating biodiversity. In this study, we monitored photographically growth, fusions, fissions, and survival of two morphologically cryptic species Hemimycale mediterranea Uriz, Garate & Agell, 2017 and H. columella (Bowerbank, 1874). Additionally, we characterized the main environmental factors of the corresponding species habitats, trying to ascertain whether some abiotic factors were correlated with the distribution of these species. Sponge monitoring was performed monthly. Seawater samples were collected the same monitoring days in the vicinity of the target sponges. Results showed contrasting growth and survival patterns for each species: H. mediterranea totally disappeared after larval release while 64% of individuals of H. columella survived the entire two years we monitored. The species also differed in the number of fissions and fusions. These events were evenly distributed throughout the year in the H. mediterranea population but concentrated in cold months in H. columella. No measured environmental factor correlated with H. mediterranea growth rates, while temperature and dissolved organic nitrogen were negatively correlated with H. columella growth rates. The strong differences in depth distribution, survival, growth, fusions, and fissions found between these two cryptic species, highlights the importance of untangling cryptic species before ecological studies are performed in particular when these species share geographical distribution.

Structure from Motion Photogrammetry as an Effective Nondestructive Technique to Monitor Morphological Plasticity in Benthic Organisms: The Case Study of Sarcotragus foetidus Schmidt, 1862 (Porifera, Demospongiae) in the Portofino MPA

“…In addition, S. foetidus' growth rate was estimated for the first time, previously only known for the congeners Sarcotragus spinosulus Schmidt, 1862 (100% year −1 ), and Sarcotragus fasciculatus (Pallas, 1766) (40.03 ± 4.81% year −1 ) [54,55], both showing higher rates of volume increase compared to our results (9.24 ± 5.47% year −1 ). As already stated, these strong differences might be related to various factors, such as the species-specific growth rate, the different ages of the surveyed organisms [13,56], or the fact that the surveyed organisms were under increasing stress conditions due to the recurrent episodes of thermal anomalies in the area. In the context of an ever-warmer Mediterranean, gradual shifts in shallow benthic communities are expected towards a dominance of thermo-tolerant species [57].…”

­Reproductive strategies of two common sympatric Mediterranean sponges:Dysidea avara(Dictyoceratida) andPhorbas tenacior(Poecilosclerida)

“…However, both species have a similar Atlanto-Mediterranean distribution ( Cruz, 2002 ; Van Soest et al, 2018 ). The reproduction timing and growth of Atlanto-Mediterranean sponges in the Mediterranean is often correlated with their geographic origin ( Blanquer, Uriz & Agell, 2008 ; Garate, Blanquer & Uriz, 2017 ) with presumably Atlantic species not reproducing in summer, the period of highest temperatures and trophic depletion ( Turon, 1988 ; Coma et al, 2000 ). The reproductive timings of the two study species suggest an Atlantic origin for D. avara , and a Mediterranean origin for P. tenacior , which should be confirmed by studies of population genetics.…”